Yeast Slant Failure #1

Let’s be honest, when it comes to the hobby of home brewing from time to time even the most studious brewing enthusiast will make mistakes. From stuck fermentations, to soured batches, and even the occasional exploded carboy history proves that we all learn the most when we can learn from our mistakes. With that in mind I present what will likely be the first in a long line of mistakes that I will make in my beer making journey in the hopes that other brewers can avoid the obvious traps into which I fell.

Therefore I present a brewers guide in how not to prepare blank yeast slants. I repeat: Do not follow these directions if you want to make functional yeast slants.

My interest is making yeast slants comes from a constant desire to increase the economical efficiency of my brewing process. Currently every time I execute a new brew I spend roughly $8.00US on a Wyeast Activator package. However, after doing some research I discovered the wonderful world of yeast slants and the ability to culture a specific yeast strain near infinitum for constant reuse. Being able to remove the $8.00US cost for each 5 gallon batch of beer translates into a saving of roughly $0.15US per 12oz bottle of beer, so why not give it a go?

I knew that I had enough equipment on hand that would in theory allow me to make a nice batch of blank yeast slants given the right ingredients. After a short search at a localish international food store I located several cheap packets of agar powder which would last me through an incalculable number of yeast slant batches. Being armed with this vital ingredient I figured that I would have everything I needed to create the blank yeast slants.

The plan to create a quarter gallon of yeast slant growth medium was as follows:

Cook up 1/4lb of inverted sugar syrup

Add 1/4 gallon of water effectively creating a sugar rich solution with a gravity of 1040

Add enough agar powder according to the package for the given liquid amount

Boil the mixture to sterilize

Pour mixture into slant containers and let solidify

Profit?

Step #1 – Invert 1/4lb of Sugar

Following the initial steps in How to make Belgian Candi Sugar I measured out 1/4lb of sugar then mixed in a pinch of cream or tartar and enough water to make a thick slurry.

Then I cooked the mixture at a temperature between 260° and 275deg; for approximately 20 minutes to ensure complete inversion of the sucrose molecules. As a lucky side effect of getting sidetracked I ended up cooking the mixture longer than expected which caramelized the sugars a bit creating a nice amber syrup.

Step #2 – Add Water and Agar According to Package

The agar I am using for this failure is Telephone Brand Agar-Agar Powder.

The package lists mixing instructions of 1 teaspoon to 500ml liquid. A bit quick bit of math shows that 16oz of liquid is 473.17ml which is close enough to the directions. So 16oz of water is added to the inverted sugar mixture along with 16oz of water.

Failure #1 – No matter how much I’d like it to be 16oz is still not 1/4 gallon.

Imperial measurements fail me again as a gallon is in fact 128oz meaning the gravity of the mixture is not a yeast friendly 1040 but instead a much more stressful 1080. Since the volume was just what I was looking for I would have done much better to invert only around 1/8lb of sugar to mix with the 16oz of water or just use a full 32oz of water with 2 teaspoons of agar power and figure out something to do with the extra growth medium.

Step #3 – Boil the Mixture to Sterilize

Needless to say the growth medium that has been created needs to be as sterile as possible, and who knows there that agar has been? Go ahead and boil the mixture for 15 minutes to sterilize everything to a state acceptable of the most germophobic individuals.

Step #4 – Sterilize Yeast Slant Containers

Although listed as step #4 this should likely occur in-line with the previous steps.

To sterilize the yeast slant containers (unused sterile-grade screw top bottles) I chose to utilize a steam sterilization methodology rather than the usually suggested pressure cooker method. Why? I don’t own a pressure cooker, any iodophor, or Star-san and didn’t feel like messing around with a full boil sterilization or bleach.

For the steam sterilization I loaded up the containers in a steamer basket and into a larger cooking pot with about an inch of water over high heat. Once steam was created the top was placed on the pot and everything was left to steam for a good 20 minutes or so. It may not be an autoclave, but it should be good enough to sterilize the containers for our needs.

The process was repeated again for the remaining airtight glass container (to be used as a makeshift petri dish) and the before-used glass measuring cup.

Step #5 – Fill Sterilized Containers with Growth Medium

Now that everything used within the process is adequately sterilized we can fill the yeast slant containers with the sterile agar growth medium and seal everything up tight. Make sure to not fill the containers over half full.

Step #6 – Slant Containers and Let Set

Now that the containers were filled all that was left was to increase the surface growth area by slanting the containers and allowing the growth medium to set. To accomplish this I just tilted everything on a set of spring loaded tongs that happened to be lying around.

Note that the mock petri dish was allowed to stand flat as no slanting was required.

Once everything was balanced at the proper angle in accordance with gravity’s laws the containers were allowed to solidify overnight.

Step #7 – Realize Obvious Mistakes. Write Failtorial.

So obviously something is wrong with these blank yeast slants which goes beyond the unplanned high gravity. The currently identified errors lie in the biological requirements of yeast and the other is the act of learning the nature of how agar sets up.

Failure #2 – Yeast rely on biological mechanisms and can not subsist on sugar alone.

This is the biggest flaw of the whole procedure. The biological processes involved in the growth and continued sustained life of yeast cells require a wide range of minerals and nutrients from free amino nitrogen (FAN) and amino acids to more basic requirements like zinc and magnesium. Unfortunately the prepared growth medium contains none of these nutritional requirements, and as such yeast growth should be either slowed or otherwise completely inhibited.

In order to fully test the magnitude to which this mistake inhibits the effective use of the blank slants I will make several more in the future utilizing the addition of a commercial yeast energizer as well as a generic multivitamin. The results will be documented and conveyed to you the reader.

Even following the directions on the package the resultant growth medium would have retained the expected desert gelatin which while possibly delicious is much too firm for adequately mixing into a gradually stepped up starter. Next time I will experiment with using half the recommended agar powder to obtain a consistency somewhere in the middle of jelly and firm tofu.

So that pretty much wraps up my first attempt and failure at creating viable blank yeast slants. Once I have a better method down I will write up an actual tutorial, but in the mean time I will still try to propagate some yeasts onto this medium just to see what happens.

I realize that this post is super long in the tooth now but I couldn’t help but wonder why you didn’t use DME for your food source in the agar? It has FAN and amino acids, well, because it’s what yeast prefer? Anyway, even if it’s a fail, we appreciate learning from your experiences! Love your articles on Cabdi sugar, it’s my go to and has saved me tons of cash!